Mullite Module for Liquid Filtration

ABSTRACT

The disclosure relates to a material suitable for forming a honeycomb monolith for liquid filtration and, more particularly, to a mullite material for forming a cross-flow filtration device for separating a feed stock into filtrate and retentate, methods for forming the filtration device, and filtration devices formed from the material.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/276,028 filed Nov. 21, 2008 entitled “Mullite Module for LiquidFiltration”, which claims the benefit of U.S. Provisional ApplicationSer. No. 61/089,718 filed Aug. 18, 2008 and entitled “Mullite Module forLiquid Filtration”.

FIELD

The disclosure relates to a material suitable for forming a honeycombmonolith for liquid filtration and, more particularly, to a mullitematerial for forming a cross-flow filtration device for separating afeed stock into filtrate and retentate, methods for forming thefiltration device, and filtration devices formed from the material.

BACKGROUND

Slotted cross-flow filtration devices have been used to separatecontaminated liquid feed stock into cleaner filtrate and retentate (see,for example, U.S. Pat. Nos. 4,781,831, 4,983,423). In applications,these devices need to stand up to liquid streams that may have high pH,low pH, contain dangerous or caustic contaminants, may be heavilycontaminated with particulate matter or non-soluble elements, as well aswithstand significant pressures. These conditions require materials thatcan withstand these chemical and physical challenges over long periodsof useful life.

SUMMARY

In embodiments, the present invention provides a mullite material forliquid filtration having suitable filtration flux while maintainingsuitable strength and corrosion durability. In embodiments, water flowof the mullite material for liquid filtration is higher than 1200 ml/minat 60 psi (or above 140 mDarcy Hg Permeability).

In embodiments, the present invention provides a mullite material forliquid filtration having greater than 30% weight percent mullite and10-15% weight percent bentenite, and optionally less than 15% finealumina, optionally between 8 and 42% coarse alumina; and optionally 2to 10% silica to a total weight percent of 100%; and a superaddition ofpore former having 10-15% graphite and 5-15% potato starch.

Embodiments of the present invention also provide a method for forming afiltration device for receiving a process stream and for separating theprocess stream into a filtrate and a retentate comprising the steps of:dry blending greater than 30% weight percent mullite and 10-15% weightpercent bentenite, and optionally less than 15% fine alumina, optionallybetween 8 and 42% coarse alumina; and optionally 2 to 10% silica to atotal weight percent of 100%; adding a superaddition of pore formerhaving 10-15% graphite and 5-15% potato starch; adding sufficient waterto form a deformable batch; extruding the batch; and sintering at atemperature of greater than 1550° C.

In a still further embodiment, the invention provides a sintered ceramicarticle made from a composition comprising greater than 30% mullite;10-15% bentonite; less than 15% fine alumina; optionally 10-42% coarsealumina; and optionally 2-10% silica; wherein the ceramic articlefurther comprises pores having a median pore diameter of 8-11 μm.

Additional embodiments and advantages of the disclosure will be setforth, in part, in the detailed description, and any claims whichfollow, or can be learned by practice of the disclosure. The foregoinggeneral description and the following detailed description are exemplaryand explanatory only and are not restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate certain embodiments of thedisclosure.

FIG. 1 is a perspective view of an exemplary monolithic body accordingto the disclosure.

FIG. 2 a is a perspective view of an exemplary monolithic body accordingto the disclosure further having a plurality of filtrate conduits formedtherein.

FIG. 2 b is a schematic cross-sectional view of the monolith body shownin FIG. 2 a, taken at plane b-b shown in FIG. 2 a.

FIG. 3 is a schematic illustration of a cross-flow filtration systemutilized in the filtration tests of Example 2.

FIG. 4 is a graph illustrating the relationship between water flow andfiltration pressure for a number of embodiments of mullite monolithbodies of the present invention.

FIG. 5 is a graph illustrating the relationship between measured Hgpermeability and water flow at 60 psi (measured in ml/min) for a numberof embodiments of the mullite monolith bodies of the present invention.

FIG. 6 is a graph illustrating durability of a number of embodiments ofthe mullite materials of the present invention in acid and baseenvironments over multiple acid/base durability test cycles.

FIG. 7 is a graph illustrating the relationship between measured HgPermeability and MOR for a number of embodiments of the mullitematerials of the present invention.

FIG. 8 is a graph illustrating the relationship between measured HgPermeability and Rod Strength MOR for a number of embodiments of themullite materials of the present invention.

FIG. 9 is a graph illustrating relationship between measured HgPermeability and Pore Diameter.

FIG. 10 is a graph illustrating Hg Permeability compared to Pore Volume.

DETAILED DESCRIPTION

Separating liquids, and separating solid particulate from liquid streamsis an important step in many industrial and manufacturing applications.Cross-flow ceramic honeycomb monoliths have been used in theseindustrial liquid filtration applications. These ceramic monoliths aremade from extrudable materials that have an appropriate porosity toallow a mixed fluid stream to enter the ceramic honeycomb monoliththrough an inlet face, and separate into a filtrate fluid stream and aretentate fluid stream. The filtrate fluid flows into the ceramichoneycomb monolith through the inlet face, flows through the walls ofthe ceramic monolith, and exits the ceramic honeycomb monolith throughthe walls of the ceramic monolith or through holes or slots in theceramic monolith into a filtrate collector. The retentate fluid flowsinto the ceramic honeycomb monolith through the inlet face, flows alongthe honeycomb flow channels of the monolith, exits the monolith at theoutlet face into a retentate collector. Membranes may be applied tosurfaces of the honeycomb monolith to allow for an additional layer ofphysical separation or chemical or catalytic separation which improvethe separation characteristics of the monolith. Mullite, cordierite andsilicon carbide (SiC), for example, may be used for these liquidfiltration applications.

To have good industrial characteristics, the material should have goodstrength and durability in challenging environments combined with higherpermeability. Challenging environments may include high pH, low pH, hightemperature, low temperature, exposure to aqueous fluids, organicfluids, reactive chemical species, or combinations of these includingfluctuations between high and low temperatures, fluctuations betweenhigh pH and low pH and mixtures of aqueous and organic materials. Acombination of good strength and durability and higher permeabilityleads to higher product filtration flux and higher throughputs withpotentially lower processing pressures and create longer product life.

High permeability generally implies higher porosity and larger poresize. A higher level of porosity is generally accompanied by a higherlevel of internal surface area, with greater exposure to corrosiveattack. In general, higher permeability corresponds to reduced strength.In embodiments of the present invention, a porous mullite membranesupport structure that may have increased filtration flux (increasedpore size or density) while maintaining other important productattributes such as strength and corrosion durability are provided.

Various embodiments of the disclosure will be described in detail withreference to drawings. Reference to various embodiments does not limitthe scope of the disclosure. Additionally, any examples set forth inthis specification are not limiting and merely set forth some of themany possible embodiments for the claimed invention.

The following description of the invention is provided as an enablingteaching of the invention in its best currently known embodiments. Tothis end, those skilled in the relevant art will recognize andappreciate that many changes can be made to the various embodiments ofthe invention described herein, while still obtaining the beneficialresults of the present invention. It will also be apparent that some ofthe desired benefits of the present invention can be obtained byselecting some of the features of the present invention withoututilizing other features. Accordingly, those who work in the art willrecognize that many modifications and adaptations to the presentinvention are possible and can even be desirable in certaincircumstances and are a part of the present invention. Thus, thefollowing description is provided as illustrative of the principles ofthe present invention and not in limitation thereof.

In this specification and in the claims which follow, reference will bemade to a number of terms which shall be defined to have the followingmeanings:

As used herein, the singular forms “a,” “an” and “the” include pluralreferents unless the context clearly dictates otherwise. Thus, forexample, reference to a component or ingredient includes embodimentshaving two or more such components, unless the context clearly indicatesotherwise.

“Optional” or “optionally” means that the subsequently described eventor circumstance can or cannot occur, and that the description includesinstances where the event or circumstance occurs and instances where itdoes not. For example, the phrase optional component or optionalingredient means that the component can or can not be present and thatthe description includes both embodiments of the invention including andexcluding the component.

Reference will now be made in detail to embodiments of the invention,examples of which are illustrated in the accompanying drawings. Wheneverpossible, the same or similar reference numerals will be used throughoutthe drawings to refer to the same or like parts. It should be notedhowever that the drawings are for illustrative purposes only and are notnecessarily drawn to scale.

Referring to FIG. 1, a monolithic multi-channel substrate 10 is shownhaving a porous monolithic body or module 150 defining a plurality offlow channels 110 disposed in the body and extending along the length ofthe substrate from an upstream inlet or feed end 1101 to a downstreamoutlet or exhaust end 1102. Porous channel walls 114 surround each ofthe plurality of flow channels 110. The porous body 150 furthercomprises a networked pore structure of interconnected pores formingtorturous fluid paths or conduits 152. The tortuous paths 152 formed bythe porous body 150 provide a flow path for separating filtrate whichflows through the porous material to an exterior surface of thesubstrate for collection in a filtrate collector, from retentate, whichflows through the flow channels to a retentate collector, separate fromthe filtrate collector. In embodiments, the filtrate may flow out of themonolith body through holes or slots in the monolith body (see FIG. 2).In embodiments, the inventive monolithic multi-channel substrate, asexemplified in the following description, can be used for liquid-phaseseparation in laboratory scale or in commercial scale, for extraction ofone or more components from a fluid process stream.

The monolithic body 150 can have any desired predetermined size andshape. For example, although the body or module 150 is exemplified as acylinder with a substantially circular cross-section in FIG. 1, itshould be understood that the module 150 can be shaped to provide anyelliptical or polygonal cross-section. To that end, exemplary andnon-limiting monolith cross-sectional shapes include ellipses, circles,rectangle, square, pentagonal, hexagonal, octagonal, and the like. Forconsistency and simplicity, the cylindrical form of the module body 150has been used primarily in the subsequent discussions.

The plurality of flow channels 110 may be distributed in parallel andsymmetrically over the module cross-section. The flow channels alsoextend from the module upstream inlet end 1101 to the module downstreamoutlet end 1102, forming a pathway through which a process stream canpass. In the exemplified embodiment, the flow channel cross-sectionalshape is circular or rounded. However, it should be understood that theflow channel cross-section shape can be any desired elliptical orpolygonal shape that is continuous and which has substantially no sharpcorners. Exemplary channel cross-sectional shapes include ellipses,circles, rectangle, square, pentagonal, hexagonal, octagonal, and thelike. Even though the channel distribution is shown uniform in FIG. 1,the flow channels 110 can be distributed within the module innon-uniform ways. In an embodiment, the flow channels are substantiallyparallel. However, depending upon the geometry of the module, flowchannels may not follow a straight course, and may not be parallel. Forexample, if there is sufficient web thickness where there would not bean overlap or intersection of non-aligned channels, the channels 110 caneven be skewed (having a skewed angle less than 90°) in a non-paralleldistribution. For a non-uniform channel distribution, the web thickness130 will be in a range of different thicknesses (for example, about 0.2to about 2 mm). It may be advantageous to have a skin thickness(e.g., >1 mm or 0.04 inch) in the rim 120 greater than the web thickness130. The skin or rim thickness 120 is an independent parameter from theweb thickness 130. The web thickness 130 is a measure of the distancebetween channels 110, while the skin or rim thickness 120 is a measureof the distance from the outside channel to the outer surface of themodule, and affects the overall module strength and permeability.

In embodiments, the monolithic body 150 can be formed from any suitableporous material including inorganic or organic materials. In someembodiments, the monolithic body can for example be comprised of apolymeric material. In other embodiments, the monolithic body can becomprised of metallic or ceramic materials. In an embodiment, themonolithic body is comprised of a porous ceramic material. For example,and without limitation, in some embodiments the porous monolith body 150is made from a ceramic composition selected from mullite (3Al₂O₃-2SiO₂),alumina (Al₂O₃), silica (SiO₂), cordierite (2MgO-2Al₂O₃-5SiO₂), siliconcarbide (SiC), aluminum titanate, alumina-silica mixture, glasses,inorganic refractory materials, ductile metal oxides, pore formers andsintering aids. Mullite, for example, has high strength, high corrosiondurability, and is easy to process.

The module or body 150 can be prepared by any conventionally knowncasting or extrusion methods. For example, the module or body can becomprised of a sintered ceramic composition having mullite as itsprimary phase. The sintered ceramic can be prepared from an extrudableplasticized batch composition comprised of ceramic forming rawmaterials, an organic binder system, and an optional liquid vehicle. Theextrudable mixture can be extruded to form a green body of the desiredconfiguration. The green body can be dried and fired for a time and attemperature sufficient to form a sintered ceramic structure. Thefiltrate conduits can be formed in the monolith, for example, at thetime of manufacture by extrusion or by other means after extrusion. Forexample, filtrate conduits may be cut into the monolith after extrusion.For processing fluid streams in applications such as coarsemicrofiltration, extraction, fluid mixing, and the like, the porousmonolith body 150 can be used by itself in the absence of an addedmembrane layer. However, for other fluid stream processing applications,a porous membrane can be deposited on at least a portion of the porousflow channel walls.

If desired, an optional intermediate layer 160 of porous materials thathave smaller pore sizes than the pores of the monolith matrix can bedeposited onto the channel wall 114 of the substrate or matrix bodyportion 150 and can be used alone or with additional layers 140. Thecoating layer 160 can serve one or more possible functions. In someembodiments, the coating 160 can be applied to modify the flow channelshape and wall texture, including such parameters as pore size, surfacesmoothness, and the like. In other embodiments, the coating layer 160can be used to strengthen the monolithic body 150. In still furtherembodiments, the coating layer 160 can be used to enhance the membranedeposition efficiency and adhesion.

When present, the porous coating layer 160 may be deposited such that itexhibits a layer thickness in the range of from about 5 to 150 μm.Further, the pore volume of the optional coating layer 160 may have poresizes in the range of from 2 nm to about 500 nm. Thus, one or moreintermediate porous coating layers 160 can optionally be disposed on theinner surfaces or walls 114 of the plurality of feed flow channels 110to form a nano- or meso-porous layer.

The optional layer 160 may be a material selected from the groupconsisting of alumina, silica, mullite, glass, zirconia, titania, and acombination of any two or more thereof. In an embodiment, theintermediate layer 160 is comprised of alumina, zirconia, silica ortitania. The intermediate coating layer 160 may be applied byconventionally known wet chemistry methods such as a conventionalsol-gel process or slip casting.

Optionally, an additional coating 140 providing a separation functioncan be further applied onto the optional intermediate coating layer 160or directly on the inner surfaces or walls 114 of the plurality of feedflow channels 110 of the monolithic body 150. To that end, because thelayer 160 can be used alone, without another layer, the term “coating”as used herein refers to embodiments comprising the use of the layer 160alone, use of the layer 140 alone, or the use of both layers 140 and160. Multiple layers of coatings may be present. The coating 140 can becomprised of inorganic or organic materials. For example, in someembodiments, the coating 140 can be a dense layer, or a non-metallicdense film that allows permeation of certain molecules in a mixture,such as SiC, or glass. In still other embodiments, the coating 140 canbe a micro-porous layer comprised of, for example, zeolite, zirconia,alumina, silica, titania, or glass. These exemplary microporous coatingmaterials can be used to provide a separation function in the molecularsize level. In still further embodiments, the coating layer 140 can be apolymeric film. When present, the porous coating layer 140 may bedeposited such that it exhibits a layer thickness in the range of fromabout 1 to 20 μm. Further, the pore volume of the optional additionalcoating layer 140 may have pore sizes less than about 200 nm.

Embodiments of monoliths made from compositions of the present inventioncan be used for separating, purifying, filtering, or other processingfunctions for a variety of liquid-phase mixtures through a plurality oftortuous paths 152 through the matrix of the porous body portion 150having coated sections 1521 and a non-coated porous body sections 1522.In general, the concept of tortuosity is defined as the differencebetween the length of a flow path which a given portion of a fluid or amixture of fluids will travel through the passage formed by the channelas a result of changes in direction of the channel and/or changes inchannel cross-sectional area versus the length of the path traveled by asimilar portion of the mixture in a channel of the same overall lengthwithout changes in direction or cross-sectional area, in other words, astraight channel of unaltered cross-sectional area. The deviations froma straight or linear path, of course, result in a longer or moretortuous path and the greater the deviations from a linear path thelonger the traveled path will be.

In embodiments, the monolith or substrate of the present invention 10has a structure that in use can be placed vertically as shown in FIG. 1,laid horizontally as shown in FIG. 3, in a slant, or aligned in anyother position. Each of the feed flow channels 110 has an upstream inletor feed end 1101 and a downstream outlet end 1102. The coatings 160 and140 are supported and adapted to receive under a positive pressuregradient 170, an impure mixed feedstream 180 fed on the feed end 1101 ofthe plurality of flow channels 110. The positive pressure gradient 170consists of first pressure drop 171 across the membrane 140 and optionalcoating layer 160 and a second pressure drop 172 through the porousmonolithic body 150. The coatings 160 and 140 is adapted to process theimpure mixed feedstream 180 into a purified filtrate or permeate 1852that is formed from a portion of the impure mixed feedstream 180 thatpasses through an outside surface of the coating 140 and into theplurality of tortuous paths 152 of the matrix of the body portion 150,entering the coated section 1521 and exiting through the non-coatedporous body section 1522. A byproduct or retentate stream 1802 remainsfrom a portion of the impure mixed feedstream 180 that does not passthrough the coated films 160 and 140 and exits through the outlet end1102 of the plurality of feed flow channels 110.

With reference to FIGS. 2 a and 2 b, in additional embodiments, themonolith 150 may contains flow channels 110 as shown in FIG. 2 a andillustrated in part of FIG. 2 b, and one or more filtrate conduits 190formed within the monolith 150 as shown in FIGS. 2 a and 2 b. Filtrateconduits are special flow channels structured and arranged to provide apathway for filtrate material to flow through the interior of themonolith in a separate stream from retentate material.

In some embodiments, the filtrate conduits 190 may extend longitudinallyfrom the upstream inlet or feed end to the downstream outlet or exhaustend of the structure. Alternatively, at least one of the filtrateconduits can extend longitudinally with the one or more flow channelsalong at least a portion of its length. As further shown in FIG. 2 b,the filtrate conduit can include a channel or slot 192 extendingtransversely from the longitudinal portion to a filtrate collection zonefor directing filtrate to the external surface of the monolith 150 or toa filtrate collection zone (see 300, FIG. 3). The filtrate conduit mayfurther include a plurality of longitudinal chambers which connect withthe channel. The slot 192 may be an opening, slot or channel at an endof the monolith or a hole formed in the monolith to connect thelongitudinal portion of the filtrate conduit to the filtrate collectionzone 300 (see FIG. 3). In embodiments, at least one slot may be formedin the filtrate conduit or slots may be formed at both the feed end andthe outlet end of the device. Or, slots 192 may be holes introducedthrough the exterior surface of the monolith body at any point along thelength of the monolith. The filtrate conduits 190 may be blocked at thefeed end and the outlet end by barriers 194. Barriers 194 inhibit directpassage of the process stream into or out of the filtrate conduits atthe feed end or the outlet end of the monolith. The barrier 194 may beplugs of material, inserted or introduced into the filtrate conduit 190.The barrier 194 may be made from the same material as the structure, orother suitable material, and the plugs may have a porosity similar to orless than that of the structure material.

In embodiments of the present invention, which provide filtrate conduits190, blocked at both a feed end 1101 and an outlet end 1102 withbarriers 194, received process stream enters the monolith 150 at theinlet end 1101 of the monolith. A portion of the received processstream, the retentate, flows through the monolith 150 through flowchannels 110, to the exit end 1102 as shown by arrow 225 in FIGS. 2 aand 2 b. A portion of the received process stream, the filtrate, entersthe monolith through flow channels 110, flows through the networked porestructure of the monolith 150, to a filtrate conduit 190, imbedded inthe monolith structure. The filtrate conduits 190 are flow channelswhich are blocked at both ends by barriers 194, and which are open tothe side of the monolith through slots or exit pathways 192 to allowfiltrate to flow through the porous structure of the monolith, tofiltrate conduits to the exterior of the monolith. Because the filtrateconduits 190 are blocked at both ends, they form low pressure pathwayswithin the monolith structure. The fraction of the process stream thatenters the pores of the monolith structure flow to this low pressurepathway through the pores of the material, and then exits the monoliththrough the slots or exit pathways 192, in a filtrate collection zone300 (see FIG. 3) which is separate from the outlet end of the monolith,from which the retentate is collected. In this way, the process streamis separated into a retentate, which flows through the monolith from theinlet end to the exit end through flow channels 110, and a filtratewhich flows into the monolith, enters the pore structure of the porousmaterial, flows into a filtrate conduit 190, and exits the monoliththrough slits 192 in the side of the monolith 150 (as shown by thearrows 226 in FIG. 2 b). The filtrate conduits 190 provide pathwayshaving a low flow resistance compared to the flow channels, creating apressure drop that allows filtrate to flow through the networked porestructure of the monolith to the filtrate conduits 190. The filtrateconduits are blocked by barriers 194 to an exterior surface of themonolith body.

The filtrate conduits 190 provide flow paths of lower flow resistancethan that of flow channels 110 through the porous material, and thestructure is constructed such that the filtrate conduits are distributedamong the passageways to provide low pressure drop flow paths from thepassageways through the porous material to nearby filtrate conduits. Theplurality of filtrate conduits can carry filtrate from within thestructure toward a filtrate collection zone 300 (Fp, see FIG. 3)disposed about the exterior surface of the monolithic body or module150. Exemplary discrete filtrate conduits 190 are for example disclosedand described in U.S. Pat. No. 4,781,831.

FIG. 3 illustrates a liquid filtration system 350 that can be used withembodiments of the present invention. The liquid filtration system 350,illustrated in FIG. 3 shows a honeycomb monolith 150 in a housing 310. Aliquid stream is pumped by a pump 320 into the inlet side of themonolith 150 in the housing 310 (Pf, m). The liquid flows through themonolith 150 and filtrate is separated out of the fluid as indicated bythe arrows. The filtrate is removed from the housing through a filtratecollection zone 300 (Fp). Retained fluid (Rf) flows out through theoutlet face of the monolith (Pf, out) and is collected in a retentionzone 340. This retentate may be recycled through the monolith, ordrained. This system can be used to perform the water flow testdescribed in Example 2.

In use, the inventive filtration device can be used for separationprocesses wherein the mixed feedstream is a liquid-phase stream, such asa water-based solution containing other larger components or a mixedwater and oil-based solution. The larger components can be largermolecules and/or particulates. For example, a water mixture can havefinely-dispersed oil droplets from an industrial waste water stream.Water mixtures can have particulates such as in a beverage juice. Watermixtures can have macro molecules such as proteins. The membranedsupport is suitable for separation processes with water as the permeate,because water as the smallest molecule the liquid mixture would have alarger permeability through the substrate matrix than the othercomponents. Moreover, the membraned support is also suitable forseparation processes of liquid mixtures involving organic solvents wherethe organic solvent is the permeate. The liquid-phase stream could be anorganic solvent-based solution containing other larger components.

In embodiments, filtrate conduits 190 may be absent (as shown in FIG. 1)or present (as shown in FIGS. 2 a and 2 b). In general, monolithsubstrates having smaller module hydraulic diameters (for example lessthan about 50 mm) provide adequate filtration without incorporatingfiltrate conduits 190. Larger substrates may require filtrate conduitsin order to facilitate the removal of filtrate fluids from the internalportions of the larger substrate.

Table I shows liquid filtration mullite compositions and their physicalproperties and performance data. Alumina, silica and mullite rawmaterial particle size and pore formers were used to createpermeability. Fine and/or reactive materials as well as sintering aidsand higher sintering temperatures were used to enhance strength andresistance to chemical attack. Physical property data, shown in Table I,were obtained using the mercury porosity determination method, standardrod and bar MOR testing and physical shrinkage measurements. Based onthis data selected samples were prepared for corrosion durability andwater flow testing, which was intended to simulate in use productperformance testing.

TABLE 1 Liquid Filtration Support - Data Summary Physical PropertiesMedian Hg Total Diameter d50-d10/ Permea- Extrusion Porosity Intrusion(Vol) d10 d90 d50 bility 2 Comp Code # % cc/g um um um % mdarcy StdMullite @ 1495 C. EJQ-166 17300 37.7 0.1969 4.2 3.0  4.9 0.29  36EJQ-166 avg data 38.9 0.2049 4.1 2.9  4.9 0.29  35 Mullite @ 1495 C.KKS-166 18698 41.1 0.2277 6.1 2.8  9.3 0.54  75 Mullite @ 1550 C.EJQ-166 19667 29.9 0.1415 4.1 3.0  4.7 0.26  26 KKS-166 18698 33.50.1598 6.5 3.4 10.7 0.48  67 NLH-102 19670 42.3 0.2353 7.8 3.9 11.4 0.50116 Mullite @ 1600 C. EJQ-166 19667 16.6 0.0652 3.9 2.9  4.7 0.24  15NLC-102 19153 28.6 0.1290 6.6 3.5 14.6 0.47  52 NLD-102 19154 33.20.1566 5.7 2.8  9.3 0.51  46 KJC-166 18199 43.3 0.2354 8.6 4.6 12.9 0.47149 NLF-102 19668 33.8 0.1619 8.9 4.9 18.8 0.46 112 NLG-102 19669 32.30.1588 7.4 3.8 12.0 0.49  74 NLH-102 19670 34.3 0.1719 8.6 4.9 17.9 0.43118 NLI-102 20846 49.6 0.3096 9.0 4.4 12.5 0.52 173 NLJ-102 20847 43.80.2544 9.4 4.8 12.8 0.49 182 NLK-102 20848 41.3 0.2295 10.7  4.8 16.70.55 213 NLL-102 22550 37.9 0.1940 9.2 4.4 14.3 0.52 141 NLM-102 2302146.8 0.2781 8.2 3.5 12.6 0.57 140 NLN-102 23338 47.5 0.2933 10.7  5.415.2 0.50 249 NLO-1-2 24880 42.2 0.2325 9.8 4.5 15.4 0.54 181 NLP-10224881 45.1 0.2707 12.7  5.5 20.7 0.57 314 Physical PropertiesPerformance Bulk Apparent Std MOR Std Shrink Durability-Rod DensityDensity Dev (rods) Dev Mask/Fired MOR Strength Comp Code g/cc g/cc psipsi psi % dia Cycle 0 Cycle 1 Std Mullite @ 1495 C. EJQ-166 1.92 3.1 1625104 167  6.9 5725 4481 EJQ-166 1.90 3.11 193 5104 167  6.4 5168 3801Mullite @ 1495 C. KKS-166 1.81 3.07 312 6052 134 13.9 **** **** Mullite@ 1550 C. EJQ-166 2.11 3.01 425 8358 469 10.5 **** **** KKS-166 2.093.15 311 9448 335 15.1 **** **** NLH-102 1.80 3.12 235 5357 257 10.1**** **** Mullite @ 1600 C. EJQ-166 2.55 3.06 1068  13250  723 14.7 ******** NLC-102 2.22 3.10 375 9146 795 16.1 **** **** NLD-102 2.12 3.17 3508267 473 13.7 **** **** KJC-166 1.8 3.24 403 6903 296  9.7 **** ****NLF-102 2.09 3.16 245 7625 297 17.0 **** **** NLG-102 2.04 3.01 486 8477343 15.2 **** **** NLH-102 2.00 3.04 422 7564 360 14.5 **** **** NLI-1021.60 3.17 121 5139 673  8.7 5193 3334 NLJ-102 1.72 3.07 157 6160 23013.2 6521 4713 NLK-102 1.80 3.06 159 5690 170 12.4 6043 4834 NLL-1021.95 3.14 361 7254 1137  14.8 8002 6440 NLM-102 1.68 3.17 322 5862 16611.0 5630 3980 NLN-102 1.62 3.09 183 5214  99  9.8 5240 3520 NLO-1-21.82 3.14 254 6710 297 13.9 6680 4980 NLP-102 1.67 3.03 190 4972 13611.4 5010 3730 Performance Durability-Rod Wet Water Flow at increasingpressure ml/min MOR Strength Pickup 15 30 45 60 >EJQ @ Comp Code Cycle 2Cycle 4 lb/in psi psi psi psi 60 psi Std Mullite @ 1495 C. EJQ-166 40673896 0.20 136 298  471  623 1.00 EJQ-166 3829 3618 0.20 135 298  469 628 0.98 Mullite @ 1495 C. KKS-166 **** **** 0.16 143 345  550  7221.11 Mullite @ 1550 C. EJQ-166 **** **** **** KKS-166 **** **** 0.13 133320  469  610 0.94 NLH-102 **** **** 0.19 215 449  795 1075 1.65 Mullite@ 1600 C. EJQ-166 **** **** **** NLC-102 **** **** **** NLD-102 ******** **** KJC-166 **** **** 0.21 327 763 1157 1513 2.33 NLF-102 ******** 0.17 173 413  661  883 1.36 NLG-102 **** **** 0.13 107 274  430 603 0.93 NLH-102 **** **** 0.14 175 435  680  903 1.39 NLI-102 31193266 0.22 415 857 1337 1787 2.75 NLJ-102 4398 4300 0.16 280 597  8971217 1.87 NLK-102 4542 4262 0.16 264 670  963 1257 1.93 NLL-102 60865874 0.12 139 337  530  725 1.11 NLM-102 3980 3890 NLN-102 3090 3110NLO-1-2 5130 4890 NLP-102 3600 3310

Table II shows mullite monolith compositions. Superior performance isnoted for compositions codes: KJC-166, NLI-102, NLJ-102, NLK-102,NLM-102, NLM-102 and NLO-102

TABLE II Code EJQ-166 NLC-102 NLD-102 KJC-166 NLF-102 NLG-102 NLH-102NLI-102 Batch Type Mullite Mullite Mullite Mullite Mullite MulliteMullite Mullite Materials Alumina-Coarse 11 um 4988 4062 4062Alumina-Fine 06 um 1473 1500 1295 758 Alumina-Coarse 16 um 2239 Mullite9000 4142 2409 3857 9000 7193 7745 3857 Ba

ite Clay 1000 2146 1928 1446 1000 100

 99

1446 Titania Silica 675 635 504 635 Feldspar 499 Total inorganic 1000010000 11500 10000 10000 10000 10000 10000 Pore Formers Graphite-Fine1000 500 1000 1000 1000 1000 1000 Graphite-Coarse Potato Starch 10001200 1000 1000 1000 1000 1000 Binders M

cellulose 600 600 600 600 600 600 600 M

cellulose 600 Sodium Stearate 100 100 100 100 100 100 100 100 CodeNLJ-102 NLK-102 NLL-102 NLM-102 NLN-102 NLO-102 NLP-102 Batch TypeMullite Mullite Mullite Mullite Mullite Mullite Mullite MaterialsAlumina-Coarse 11 um 892 3062 Alumina-Fine 06 um 892 950 1000 950Alumina-Coarse 16 um 2779 1295 2779 Mullite 6256 8600 4175 3857 71938600 4175 Ba

ite Clay 1471 1400 1423 1446 1008 1400 1423 Titania 237 237 Silica 490436 635 504 436 Feldspar Total inorganic 10000 10000 10000 10000 1000010000 10000 Pore Formers Graphite-Fine 1000 1000 Graphite-Coarse 10001000 1000 1500 1500 Potato Starch 1500 1000 1000 1000 1000 1000 1000Binders M

cellulose 600 600 M

cellulose 600 600 600 600 600 Sodium Stearate 100 100 100 100 100 100100

indicates data missing or illegible when filed

The materials shown in Table II include inorganic materials, poreformers or burnout materials and organic binders and lubricants. Theinorganic materials shown in Table II were combined in percent by weightto form a total inorganic mixture of 100%. Pore formers were added inweight percent as superadditions to the 100% inorganic mixture. Inembodiments of the present invention, fine alumina may be a-alumina. Inembodiments, the fine alumina ingredient may have a median particle size(d50) of less than 1 μm. In exemplary embodiments, fine alumina wasA1000SGD® with a median particle size of 0.6 μm available from Alcoa(Pittsburgh, Pa.). In embodiments the coarse alumina ingredient may havea median particle size (d50) of between 5 and 20 μm, or between 10 and20 μm. In exemplary embodiments of the present invention, coarse aluminawas A10 with a median particle size of 11 μm available from Almatis(Frankfurt, Germany) and/or T64-325M with a median particle size of 16μm, also available from Almatis. In embodiments, mullite is a mullitepowder having an average particle size of less than about 50 μm or lessthan about 30 μm. In exemplary embodiments of the present invention,mullite was Mulcoa® 70-325 available from C-E Minerals (King of Prussia,Pa.). In embodiments, the water swelling clay may be a bentenite-typeclay. In exemplary embodiments of the present invention, the waterswelling clay is Bentenite L available from Southern Clay Products(Gonzales, Tex.). In embodiments, titania may be a rutile titaniumdioxide. In exemplary embodiments, titania was TiPure R-101 availablefrom DuPont (Wilmington, Del.). In embodiments, fine silica may have amedian particle size of between 2 and 10 μm. In exemplary embodimentssilica was Im-sil A-25 available from Unimin (New Canaan, Conn.). Inembodiments, feldspar may be a potassium/sodium/calcium aluminumsilicate ground to about 200 mesh for ceramic applications. In exemplaryembodiments, feldspar was G-200 available from Feldspar Corp (Edgar,Fla.). In embodiments, graphite and potato starch are pore formers orburnout materials. In exemplary embodiments, graphite is 4602-(A625)graphite and 4740 graphite available from Asbury (Asbury, N.J.). Inexemplary embodiments, potato starch (white bag) can be obtained from,for example, National Starch and Chemical Company, Bridgewater, N.J. orEmsland Starke, Emlichheim Germany. In additional embodiments, poreformers such as rice starch, walnut shell flour or other materials canbe used as a pore former. In embodiments, organic binders includemethylcellulose and derivatives thereof. In exemplary embodiments,methylcellulose was Methocel A4M® and Methocel F240M® available from DowChemical (Midland, Mich.). In embodiments, lubricants include, forexample, sodium stearate. In exemplary embodiments, the lubricant wasLiga®, available from Peter Greven (Munstereifel, Germany).

In embodiments of the present invention, the pore formers include anymaterial that burns out of the composition upon sintering. In exemplaryembodiments the pore formers are graphite and potato starch, but anymaterial may be used. For example, rice starch or walnut shell flour maybe used. Each of these pore formers creates pores having differentcharacteristics and sizes. Potato starch, for example, creates largerpores. In embodiments of the present invention, it is found that 10-30%pore former creates pores in the sintered material that have desirablecharacteristics. More than 30% pore former leads to higher porosity, andreduces the strength of the material. Less than 10% pore former createsa material with reduced porosity and leads to a material with less thandesirable permeability. In additional embodiments, a pore former elementis present in a combination of graphite and potato starch where thegraphite is present in a range of 5 to 10% and the potato starch ispresent in the range of 5 to 20%. In additional embodiments, the poreformer is graphite and potato starch combined to create 20% pore former.According to embodiments of the disclosure, the total pore volume orporosity % P of the ceramic monolith may be in the range of from 10 to60%, from 20 to 60%, from 30 to 60%, from 35 to 60%, from 40 to 60% orfrom 40 to 50%, including exemplary porosity values of 37.9%, 41.3%,42.2%, 43.3%, 43.8%, 46.8% and 49.6%. Still further, the total porosityof the ceramic monolith can also be within a range derived from any twoof the aforementioned porosity values.

In embodiments, the pore volume or total intrusion (in cc/g) may be from0.10-0.40 cc/g, from 0.15-0.35 cc/g, from 0.18 to −0.32 cc/g, 0.2-0.30cc/g, including exemplary pore volumes of 0.1940, 0.2325, 0.2354,0.2295, 0.2544, 0.2781, and 0.3096. In still further embodiments, thetotal porosity of the monolithic body can be in a range derived from anytwo of the above mentioned porosity values.

FIG. 4 is a graph illustrating the relationship between water flow andincreasing filtration pressure for a number of embodiments of themullite materials of the present invention. Most mullite compositionswhich represent embodiments of the present invention have improved waterflow performance with increasing process pressure compared to the EJQstandard material. The test samples were core drilled from coated 5.66″monoliths.

The pore size and total porosity % P are values that can be quantifiedusing conventionally known measurement methods and models. For example,the pore size and porosity can be measured by standardized techniques,such as mercury porosimetry. FIG. 5 is a graph illustrating therelationship between measured Hg Permeability and water flow in psi(measured in ml/min) for a number of embodiments of the mullitematerials of the present invention. All Hg permeability measurementswere taken using a Micrometrics Autopore IV 9520 Mercury Porosimeter. Inan embodiment, a Hg Permeability Target was chosen at 140 mDarcy. Ingeneral, to achieve twice the water flow of the standard (EJQ)composition, the Hg permeability limit must be set at approximately fourtimes that of the standard. Therefore the Hg permeability target was setat 140 mDarcy (See dotted lines in FIGS. 5, and 7-10). Material exampleswith a Hg Permeability Target at or above 140 mDarcy are considered tobe desirable compositions. However, embodiments of the present inventionmay deviate from this target. This Hg permeability limit is equivalentto approximately twice the water flow of the standard EJQ when using theapplication based water flow test.

FIG. 6 is a graph illustrating durability of a number of embodiments ofthe mullite materials of the present invention in acid and baseenvironments over multiple durability test cycles. In acid and baseenvironments the strength of mullite MOR (modulus of rupture in psi)rods decreases, then levels off somewhat within the multiple cyclingintervals. Several compositions have higher strength than the standardafter four cycles. The four cycle strength limit was set at 3900 psi,equal to that of the standard EJQ after four cycles. FIG. 6 showsseveral compositions that show improved MOR characteristics compared tothe standard EJQ sample based on the four cycle MOR data.

FIG. 7 is a graph illustrating the relationship between measured Hgpermeability (shown in FIG. 5) and MOR (shown in FIG. 6) for a number ofembodiments of the mullite materials of the present invention.Compositions that showed a measured Hg permeability greater than 140(four times the EJQ standard, from FIG. 5, the target) and a four cyclemeasured MOR greater than that shown by the EJQ standard (from FIG. 6,the target) were identified. Several compositions, NLM, NLK, NLJ, NLO,and NLL, meet or exceed the 4 cycle durability strength target and theHg Permeability target.

FIG. 8 is a graph illustrating the relationship between measured Hgpermeability and rod strength MOR for a number of embodiments of themullite materials of the present invention. Relative Hg permeability andMOR strength limits were set based on successful water flow andcorrosion durability performance test data. Permeability and rodstrength MOR were measured after the 4-cycle durability test. In generalthe four cycle durability test is passed when the mullite compositionhas a starting MOR strength (before passing through the 4-cycledurability test) of 5500 psi or above. FIG. 8 shows Hg permeability withthe initial rod MOR strength. In embodiments of the present invention,the compositions that meet our application based water flow andcorrosion durability tests are also shown here to meet the limits setfor Hg permeability and initial MOR strength. More physical propertydata is available using the more generic Hg permeability and initial MORstrength tests.

FIG. 9 is a graph illustrating relationship between measured Hgpermeability and pore diameter, and illustrating that embodiments ofmullite materials of the present invention having a range of porediameters between about 8.0 μm and about 11.0 μm provide a good range ofpermeability and strength profiles.

FIG. 10 is a graph illustrating Hg permeability compared to pore volume,and illustrating that embodiments of mullite materials of the presentinvention having a range of pore volume of between about 0.2079 cc/g andabout 0.2780 cc/g (dotted vertical lines) provide a good range ofpermeability and strength profiles based on Hg permeability and initialMOR strength targets. EJQ, the standard mullite (control) showed apermeability of approximately 0.2049 cc/g. In embodiments, mullitematerials of the present invention have a pore volume between about0.185 and 0.30 cc/g.

In embodiments of the present invention, improved compositions ofmullite result in an increased filtration permeability of up to 2×compared to standard mullite materials (EJQ) as measured by the waterflow test illustrated in FIG. 3, and shown in FIG. 4.

In embodiments, the compositions of the present invention, shown inTable II, have the following raw material characteristics. Using mullite(Mulcoa 70-325) as the base material for the mullite compositions, thekey materials for balancing both permeability and strength are waterswellable clay (bentenite) (10-15%) as a pore former and sintering aide,coarse alumina (10-40%) as a pore former, fine alumina (10% or less) asa sintering aide, graphite (5-10%) as a pore former for fine connectedpores and starch (10-15%) as a pore former which yields more coarsepores for permeability. In embodiments, ranges of these materials togive a mullite monolith with the desired permeability and strength are:10-15% water swellable clay (bentenite); 10% or less fine alumina;10-40% coarse alumina; 20% pore former; 5%-10% graphite, and 10%-15%starch.

EXAMPLES

To further illustrate the principles of the present invention, thefollowing examples are put forth so as to provide those of ordinaryskill in the art with a complete disclosure and description of howembodiments of the porous monolithic substrates of the present inventionare made and evaluated. They are intended to be purely exemplary of theinvention and are not intended to limit the scope of what the inventorsregard as their invention. Unless indicated otherwise, parts are partsby weight, temperature is ° C. or is ambient temperature, and pressureis at or near atmospheric.

Example 1 Preparation of Monoliths and Monolith Samples

A ram extrusion process was used to form 5.66″ diameter honeycombmonolith structures with ˜100 cells per square inch and ˜0.24″ wallthickness (dependent on material shrinkages) for each example asdisclosed in Table II. Mulcoa 70-325 was used as the base material forthe mullite compositions. Rods were also made for strength measurements.The basic process consisted of dry blending the materials, in theproportions defined in table II above, for 5 minutes in a Littlefordmixer, then using a mix/muller to add sufficient amount of water to forma plastic deformable batch. A 200 ton Loomis ram extruder was then usedto de-air and plasticize and finally extrude the 5.66″ diameterhoneycomb. The honeycombs were microwave dried then sintered in a gas orelectric kiln to 1495° C., 1550° C. or 1600° C. These honeycombs wereused to generate the data shown in FIGS. 4-10.

In embodiments, the sintering temperature may be a key component inmaintaining the material strength while increasing permeability. Below asintering temperature of 1600° C. very few combinations of pore formersand sintering aids would yield the desired performance properties. TableI shows some materials sintered at 1495° C. and 1550° C. The KKScomposition appeared to have sufficient strength but insufficientpermeability after sintering at 1495° C. and NLH was slightly less thanoptimal on both strength and permeability after sintering at 1550° C.

Full size ˜5.66″ diameter by 10″ length monoliths were coated. Thecoating layer was a mixture of coarse and fine alumina powder, mixedwith water and polymeric binder (polyvinyl alcohol) and adjusted to a pHof about 3.5 to create a stable suspension. Parts were coated using aslip cast process, dried, and fired to adhere the membrane to thesupport. One inch diameter×2 inch length samples were core drilled outof the supports for water flow testing. From these selected samples coredrilled test monoliths were used to simulate liquid filtration flowimprovements using a “water flow” test, run at several processpressures. FIG. 4 shows several compositions that have improved waterflow with increasing process pressures over the standard EJQcomposition.

Example 2 Water Flow Test

Water flow testing was conducted using a cross-flow filtration apparatusas illustrated in FIG. 3. The pressure inside the membrane channel,P_(f), is controlled at a higher value than that in the exterior of themembrane body, P_(o). As a result, the water permeates through themembrane and comes out of the monolith body perimeter skin. Thepermeation flow rate, F_(p), was measured and recorded. Water waspumped/circulated through the monolith sample at a constant pressure.The flow through the cell wall at that pressure was measured. Flow wasmeasured at four pressures, 15 psi, 30 psi, 45 psi and 60 psi. Flux wascalculated by the following equations where F_(p)=permeation flow rateand SA_(m)=membrane surface area:

${Flux} = \frac{F_{P}}{{SA}_{m}}$

Example 3 Corrosion Test

A corrosion durability test was performed on rods of the selectedcompositions, made according to Example 1. The durability test consistedof four cycles. Each cycle included 24 hours at 95° C. in 0.5 pH HNO₃and 24 hours at 95° C. in 13.5 pH NaOH. Rod strength was then measuredafter each cycle. FIG. 6 shows several compositions with equal orgreater MOR strength after durability cycling when compared to thestandard EJQ mullite.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the present invention toinclude processing applications, such as sensors, without departing fromthe spirit and scope of the invention. Thus it is intended that thepresent invention cover the modifications and variations of thisinvention provided they come within the scope of the appended claims andtheir equivalents.

1. A composition for forming a filtration device for receiving a processstream and separating the process stream into a filtrate and aretentate, the composition comprising: greater than 30% wt. mullitepowder; 10-15% wt. bentonite; and a super addition of 10-30% wt. poreformer, wherein the pore former is a combination of graphite and potatostarch
 2. The composition of claim 1 wherein the pore former comprises10-15% wt. graphite and 5-15% wt. potato starch.
 3. The composition ofclaim 1 comprising approximately 86% mullite powder and approximately14% bentonite.
 4. The composition of claim 1 comprising approximately86% mullite powder, approximately 14% wt. bentonite, and wherein thepore former comprises 10-15% wt. graphite and 5-15% wt. potato starch.5. The composition of claim 1 wherein the pore former comprises 5-10%wt. graphite.
 6. The composition of claim 1 wherein the pore formercomprises 5-15% wt. potato starch.